1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an array substrate for an LCD and a manufacturing method thereof.
2. Discussion of the Related Art
The rapid development of an information-oriented society has generated a need for flat panel displays having characteristics such as a slim profile, light weight, and low power consumption. Liquid crystal display (LCD) devices are under active development for employment as flat panel displays because LCD devices have excellent color reproduction.
Typically, an LCD device includes two substrates each having electrodes on one surface. The two substrates are arranged such that the surfaces having the electrodes thereon face each other, and a liquid crystal (LC) layer is interposed between the two substrates. By applying a voltage across the electrodes, an electric field is generated between the electrodes. The electric field changes the alignment of liquid crystal molecules in the liquid crystal layer thus changing light transmittance through the LCD device to display an image.
LCD devices may be of various types. Active matrix (AM)-LCD devices having thin film transistors (TFTs) and pixel electrodes connected to the TFTs arranged in a matrix are in the limelight because AM-LCD devices have excellent resolution and excel at displaying moving images.
In an LCD device, the pixel electrodes are formed on an array substrate, which is the lower substrate, and a common electrode is formed on a color filter substrate, which is the upper substrate. The LCD device drives the LC molecules using a vertical electric field applied between the upper substrate and the lower substrate. The LCD device has excellent transmittance and aperture ratio characteristics, and the common electrode formed on the upper substrate serves as a ground, so that destruction of an LC cell caused by static electricity can be prevented.
The upper substrate of the LCD device further includes a black matrix (BM) to prevent light leakage occurring through the transmission of light by portions of the LCD device other than the pixel electrodes.
The array substrate, which is the lower substrate of the LCD device, is formed by repeatedly performing photolithographic process including depositing a thin layer of a material and etching the thin layer using a mask. Generally, four or five masks are used, with the number of masks representing the number of photolithographic processes used for manufacturing an array substrate.
A related art array substrate for an LCD device and a manufacturing method thereof will be described with reference to the accompanying drawings.
FIG. 1 is a plan view of an array substrate for a related art LCD device, and FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1.
Referring to FIGS. 1 and 2, in the array substrate for the LCD device, a horizontal gate line 121 and a gate electrode 122 extending from the gate line 121 are formed on a transparent insulation substrate 110.
A gate insulation layer 130 is formed on an entire surface of the transparent insulation substrate 110 including the gate line 121 and the gate electrode 122, and an active layer 141 and ohmic contact layers 151 and 152 are sequentially formed on the gate insulation layer 130.
A data line 161 perpendicularly crossing the gate line 121, a source electrode 162 extending from the data line 161, a drain electrode 163 facing a source electrode 162 with the gate electrode 122 interposed therebetween, and a capacitor electrode 165 overlapping the gate line 121 are formed on the ohmic contact layers 151 and 152.
The data line 161, the source and drain electrodes 162 and 163, and the capacitor electrode 165 are covered with a passivation layer 170. The passivation layer 170 has a first contact hole 171 and a second contact hole 172 exposing the drain electrode 163 and the capacitor electrode 165, respectively.
A pixel electrode 181 is formed on a portion of the passivation layer 170 located in a pixel region defined by gate lines and data lines crossing each other. The pixel electrode 181 is connected to the drain electrode 162 and the capacitor electrode 165 via the first and second contact holes 171 and 172.
The array substrate for an LCD device of the related art having the above-described construction can be manufactured through photolithographic processes using five masks. The photolithographic process includes various processes such as cleaning, coating of a photosensitive layer, exposure and development processes, and etching.
When the number of photolithographic processes is reduced, manufacturing time is considerably reduced, manufacturing costs are reduced, and the percentage of manufactured devices having defects is reduced. Accordingly, it is desirable to reduce the number of masks used to manufacture an array substrate.